My U.S. Application Ser. No. 954,689, now U.S. Pat. No. 4,233,029, entitled "Liquid Transport Device and Method", filed on Oct. 25, 1978, describes liquid transport members in which capillary attraction of the liquid between two opposed surfaces is used to distribute and transport the liquid. In that application, embodiments of such transport members are described for use with ion-selective electrodes (hereinafter ISE's). Such members have two opposed liquid transport surfaces spaced apart a distance effective to induce capillary flow of introduced liquid between the surfaces and to form with the surfaces a transport zone. The members further include two access apertures extending from an exterior surface of the member inwardly through one of the transport surfaces to the zone and liquid passageways from the zone to the electrodes. Effective, rapid spreading occurs when two drops are deposited within the zone, whereby an ion junction is provided. When the opposed surfaces are grooved in certain preferred configurations, the wave fronts of the spreading liquid can be readily controlled to follow predictable configurations.
Although the described device provides an effective ion bridge, it has been discovered that under certain circumstances, the flow within the transport zone can be too rapid for optimum results. If the rate of flow is too fast, any unintentional delay between the initiation of flow of the first drop and the initiation of flow of the second drop can result in the first drop reaching the aperture of the second drop before the latter is deposited. Contamination of the ISE for the second drop then occurs.
This invention has been developed to provide a solution to the aforementioned aspects.